// This is similar to the previous `from_into` exercise. But this time, we'll
// implement `FromStr` and return errors instead of falling back to a default
// value. Additionally, upon implementing `FromStr`, you can use the `parse`
// method on strings to generate an object of the implementor type. You can read
// more about it in the documentation:
// https://doc.rust-lang.org/std/str/trait.FromStr.html

use std::num::ParseIntError;
use std::str::FromStr;

#[derive(Debug, PartialEq)]
struct Person {
    name: String,
    age: u8,
}

// We will use this error type for the `FromStr` implementation.
#[derive(Debug, PartialEq)]
enum ParsePersonError {
    // Incorrect number of fields
    BadLen,
    // Empty name field
    NoName,
    // Wrapped error from parse::<u8>()
    ParseInt(ParseIntError),
}

// TODO: Complete this `From` implementation to be able to parse a `Person`
// out of a string in the form of "Mark,20".
// Note that you'll need to parse the age component into a `u8` with something
// like `"4".parse::<u8>()`.
//
// 步骤：
// 1. 按照字符串中的逗号进行分割。
// 2. 如果分割操作返回的元素少于或多于2个，则返回错误 `ParsePersonError::BadLen`。
// 3. 使用分割操作的第一个元素作为名字。
// 4. 如果名字为空，则返回错误 `ParsePersonError::NoName`。
// 5. 将分割操作的第二个元素解析为 `u8` 类型的年龄。
// 6. 如果年龄解析失败，则返回错误 `ParsePersonError::ParseInt`。

impl FromStr for Person {
    type Err = ParsePersonError;

    fn from_str(s: &str) -> Result<Self, Self::Err> {
        let vec: Vec<&str> = s.split(',').collect();

        if vec.len() < 2 || vec.len() > 2 {
            return Err(ParsePersonError::BadLen);
        }

        let name = vec[0].trim().to_string();
        if name.is_empty() {
            return Err(ParsePersonError::NoName);
        }

        match vec[1].trim().parse::<u8>() {
            Ok(age) => Ok(Person { name, age }),
            Err(e) => Err(ParsePersonError::ParseInt(e))
        }
    }
}

fn main() {
    let p = "Mark,20".parse::<Person>();
    println!("{p:?}");
}

#[cfg(test)]
mod tests {
    use super::*;
    use ParsePersonError::*;

    #[test]
    fn empty_input() {
        assert_eq!("".parse::<Person>(), Err(BadLen));
    }

    #[test]
    fn good_input() {
        let p = "John,32".parse::<Person>();
        assert!(p.is_ok());
        let p = p.unwrap();
        assert_eq!(p.name, "John");
        assert_eq!(p.age, 32);
    }

    #[test]
    fn missing_age() {
        assert!(matches!("John,".parse::<Person>(), Err(ParseInt(_))));
    }

    #[test]
    fn invalid_age() {
        assert!(matches!("John,twenty".parse::<Person>(), Err(ParseInt(_))));
    }

    #[test]
    fn missing_comma_and_age() {
        assert_eq!("John".parse::<Person>(), Err(BadLen));
    }

    #[test]
    fn missing_name() {
        assert_eq!(",1".parse::<Person>(), Err(NoName));
    }

    #[test]
    fn missing_name_and_age() {
        assert!(matches!(",".parse::<Person>(), Err(NoName | ParseInt(_))));
    }

    #[test]
    fn missing_name_and_invalid_age() {
        assert!(matches!(
            ",one".parse::<Person>(),
            Err(NoName | ParseInt(_)),
        ));
    }

    #[test]
    fn trailing_comma() {
        assert_eq!("John,32,".parse::<Person>(), Err(BadLen));
    }

    #[test]
    fn trailing_comma_and_some_string() {
        assert_eq!("John,32,man".parse::<Person>(), Err(BadLen));
    }
}
